1. Field of the Invention
The present invention relates generally to a vehicular height regulation system for regulating vehicular body height level relative to a road surface. More specifically, the invention relates to a vehicular height regulation system which has a capability of suppressing vehicular attitude change, such as rolling, pitching and lifting.
2. Description of the Background Art
In the recent days, various vehicular height regulation systems have been developed and proposed. Such vehicular height regulation systems have been known to be useful for improving riding comfort by avoiding substantial change of vehicular height or attitude, for preventing head lamp beam axis from offsetting from normal position, and for proving driving stability by adjusting vehicular height depending upon the vehicle traveling speed.
For example, Japanese Patent First (unexamined) Publication (Tokkai) Showa 57-172808, published on Oct. 23, 1982, and Japanese Patent First (unexamined) Publication (Tokkai) Showa 58-8415, published on Jan. 18, 1983 disclose typical and fundamental vehicular height control systems, in which vehicular height level is monitored at respective positions of vehicular body, for which suspension systems are provided.
On the other hand, Japanese Patent First (unexamined) Publication (Tokkai) Showa 60-85007 discloses pneumatic vehicular height regulation system which has a capability of suppressing attitude change of the vehicular body. In the disclosed system, front-left and front-right suspension systems are respectively provided variable pressure pneumatic springs connected to a pressurized air source via separately provided air supply network. On the other hand, rear-left and rear-right suspension systems have pneumatic springs connected to the pressurized air source via a common air supply network. Similarly type of vehicular height regulation system has been proposed in a co-pending U.S. patent application Ser. No. 135,110, filed on Dec. 18, 1987, assigned to common assignee to the present invention, counterpart German Patent Application has been published as German Patent First Publication No. 37 43 093.
Such prior proposed system takes a strategy of performing anti-rolling control utilizing front suspension systems and performing anti-pitching control utilizing front and rear suspension systems. Anti-rolling and anti-pitching control performed by the conventional vehicular height regulation system are successfully in suppression of vehicular attitude change in some extent. However, these controls are not at all complete and can cause degradation of drivability of the vehicle in certain condition. For example, when vehicular attitude change in rolling direction is cause due to destroy of load balance. In such case, anti-rolling control is performed only for front-left and front-right suspension system. This creates substantial difference in cornering force of the left and right suspension system to cause variation of steering characteristics.